JAR (Java Archive)

Points

• Package is the collection of classes whereas JAR is the collection of package s.
• JAR file format is platform-independent.
• You can compress and bundle multiple files associated with a Java application into a single file called a JAR file.
• JAR is based on ZIP algorithm.

JAR Syntax

jar-cf <NameOfJARFile> <Pack1> <Pack2> ...

jar-cvf <NameOfJARFile> <Pack1> <Pack2> ...

Example

jar-cf javaworld.jar

Static Import Ambiguity Flow

Important Notes

Concept	Description
Static Import	Imports public static members
Ambiguity	Occurs when same member exists in multiple classes
Normal Import	Requires class name to access members
Math.*	Commonly used static import
JAR File	Bundle of package s/classes
JAR Format	Platform independent

Package Structure Example with Multiple Packages

Directory Structure

Student.java

package com.javaindia.p1;

public class Student {

  public int sid;
  public String sname;

  public void show() {
    System.out.println("Student -> show()");

    System.out.println(sid + "\t" + sname);
  }
}

Employee.java

package org.sd.p2;

public class Employee {

  public int eid;
  public String ename;

  public void show() {
    System.out.println("Employee -> show()");

    System.out.println(eid + "\t" + ename);
  }
}

Lab484.java

package com.javaindia.p3;

import com.javaindia.p1.*;
import org.sd.p2.*;

public class Lab484 {

  public static void main(String args[]) {
    Student st = new Student();

    st.sid = 99;

    st.sname = "Midhun";

    st.show();

    Employee emp = new Employee();

    emp.eid = 88;

    emp.ename = "Nivas";

    emp.show();
  }
}

Explanation

Imported Packages

import com.javaindia.p1.*;
importorg.sd.p2.*;

• Imports all accessible classes from:
  • com.javaindia.p1
  • org.sd.p2

Objects Created

Student Object

Student st=new Student();

Employee Object

Employee emp=new Employee();

Expected Output

Student -> show()
99    Midhun

Employee -> show()
88    Nivas

Package Access Flow

Important Notes

Concept	Description
package	Defines namespace
import package.*	Imports all accessible classes
Multiple package s	Can be imported together
Public classes	Accessible from other package s
JAR structure	Stores compiled package hierarchy

Creating and Using JAR Files

Example Commands

D:\JavaWorld\MyJAR>

javac -d . *.java

jar-cf javaworld.jar com org

OR

javac -d . *.java

jar-cvf javaworld.jar com org

Compiling from Another Location

D:\JavaWorld\D1>

javac -d . Lab484.java

Result

Gives Error

Reason

• The javaworld.jar file is not available in the current location.
• Therefore compiler/JVM cannot access package classes inside the JAR.

Setting CLASSPATH for JAR File

SETCLASSPATH=%CLASSPATH%;D:\javaworld\myjar\javaworld.jar;

After Setting CLASSPATH

javac -d . Lab484.java

Output

Compiles Successfully

Running the Program

java com.javaindia.p3.Lab484

Output

Runs Successfully

Creating the EXECUTABLE JAR File

Important Points

• When the JAR file is executable, you must specify the Main-Class.
• Main class information is stored inside MANIFEST.MF.
• When JVM executes the JAR, it searches for the main class in MANIFEST.MF.
• To specify manifest information, create a text file containing main class details.

Folder Structure

JAR Creation Flow

Important Notes

Concept	Description
jar -cf	Creates JAR file
jar -cvf	Creates verbose JAR
CLASSPATH	JVM search path for classes/JARs
Executable JAR	JAR containing Main-Class
MANIFEST.MF	Stores metadata about JAR
Main-Class	Entry point of executable JAR

Lab485.java

package com.javaindia.p1;

import javax.swing.JOptionPane;

public class Lab485 {

  public static void main(String[] args) {
    String val1 = JOptionPane.showInputDialog("Enter first int Value");

    String val2 = JOptionPane.showInputDialog("Enter second int Value");

    int a = Integer.parseInt(val1);

    int b = Integer.parseInt(val2);

    int c = a + b;

    String msg = "Sum of " + a + " and " + b + " is " + c;

    JOptionPane.showMessageDialog(null, msg);
  }
}

minfo.txt

Main-Class: com.javaindia.p1.Lab485

Compile the Java Class

javac -d . Lab485.java

Create the JAR File

jar-cvmf minfo.txt javaworld.jar com

Explanation of Options

Option	Meaning
c	Create JAR
v	Verbose output
m	Include manifest file
f	Specify JAR file name

Execute the JAR File

Method 1

java-jar javaworld.jar

Method 2

• Double click the executable JAR file.

Extract JAR File

jar-xvf javaworld.jar

Explanation

Option	Meaning
x	Extract
v	Verbose
f	File name

Execution Flow

Application Flow

Important Notes

Concept	Description
JOptionPane	Used for GUI dialogs
Integer.parseInt()	Converts String to int
Manifest File	Stores Main-Class information
Executable JAR	Runs directly using java -jar
jar -cvmf	Creates executable JAR with manifest
jar -xvf	Extracts JAR contents